Add configuration rules, refactor settings management, and enhance import functionality

- Introduced a new configuration file `.cursorrules` to define coding standards, error handling, testing requirements, and project-specific guidelines.
- Refactored `config.py` to implement a `Settings` dataclass for better management of environment variables, improving testability and maintainability.
- Updated the import duty schedule handler to utilize session management with `session_scope`, ensuring proper database session handling.
- Enhanced the import service to streamline the duty schedule import process, improving code organization and readability.
- Added new service layer functions to encapsulate business logic related to group duty pinning and duty schedule imports.
- Updated README documentation to reflect the new configuration structure and improved import functionality.

tests/test_duty_schedule_parser.py

@@ -9,7 +9,6 @@ from importers.duty_schedule import (
     UNAVAILABLE_MARKER,
     VACATION_MARKER,
     DutyScheduleParseError,
-    DutyScheduleEntry,
     parse_duty_schedule,
 )
 
@@ -32,7 +31,11 @@ def test_parse_valid_schedule():
     assert "Petrov P.P." in by_name
     # Ivanov: only duty (б, Б, в) -> 2026-02-18, 19, 20
     ivan = by_name["Ivanov I.I."]
-    assert sorted(ivan.duty_dates) == [date(2026, 2, 18), date(2026, 2, 19), date(2026, 2, 20)]
+    assert sorted(ivan.duty_dates) == [
+        date(2026, 2, 18),
+        date(2026, 2, 19),
+        date(2026, 2, 20),
+    ]
     assert ivan.unavailable_dates == []
     assert ivan.vacation_dates == []
     # Petrov: one Н (unavailable), one О (vacation) -> 2026-02-17, 18